Fue unit squares are placed edge to edge as shown. What is the length of the line PQ?

Step-by-step explanation:

Given:
2 yellow flags
3 green flags
5 red flags

for a total of 10 flags.

It is a permutation of 10 objects, not all distinct.

The number of permutation is: 
     10!            3,528,800
=    = 2,520
2! * 3! * 5!        1,440

There are 2,520 different signals that can be made using the given flags.